U.S. Pat. No. 4,589,052 entitled a "DIGITAL I.sup.2 T PICKUP, TIME BANDS AND TIMING CONTROL CIRCUITS FOR STATIC TRIP CIRCUIT BREAKERS" discloses a solid state circuit interrupter employing a digital electronic trip unit. Such electronic trip units are used in circuit interrupters for acting on a number of programmed parameters to interrupt a protected circuit in a timely manner. One such electronic trip unit which allows user interaction for selecting and viewing trip parameters is found within U.S. Pat. No. 4,672,501 entitled "Circuit Breaker and Protective Relay Unit."
U.S. Pat. No. 4,870,531 entitled "Circuit Breaker with Removable Display and Keypad" describes an electronic circuit interrupter which contains a keypad and display device capable of displaying the stored circuit breaker settings. The keypad and display removably connects with the electronic trip unit within the circuit interrupter by means of a plug-in connector.
Such keypad and display units provide display capability for all possible circuit interrupter options while displaying only those parameters for which the electronic trip unit is configured by means of software located within the trip unit microprocessor. However, with such keypad and display units, the stored trip unit settings are subject to tampering since the exposed keypad actuating buttons are accessible to unauthorized personnel.
It would be advantageous to prevent unauthorized user access to the trip unit settings in order to preserve the distribution system coordination. One purpose of this invention is to prevent the changing of trip unit settings by unauthorized personnel while still allowing authorized operator access.